The fast-pass system is embedded in every Disney park. Just do a search on it to get a detailed explanation.

In a nutshell, you can get a "ticket" that allows you to return to a particular attraction between a certain time. This will get you into a line that theoretically has a much shorter wait time. It's good for the really popular attractions and marginally useful for the less popular ones.

In the beginning, you could kind of game the system and get multiple fast-pass tickets for multiple attractions at the same time. Now, there's a wait period before you can get the next one. Not all attractions have a fast-pass system but virtually all of the popular ones do.